Cold plugs

[roadrunnerron]

How does one tell if they should use regular spark plugs or cold plugs in an engine? Is it trial and error? I have a 383HP running headers, a mild cam and a trannie with a stall convertor.

 

[Hemi 354]

Why do you think colder plugs are needed? Any issues?

 

[lewtot184]

plugs that get dirty/fouled in a short time may need to be changed to something hotter. a lot of times the tune-up in general is the culprit. engines that operate at high rpms for longer durations may require a colder plug. a lot of variables.

 

[roadrunnerron]

Why do you think colder plugs are needed? Any issues?

Car starting to run crappy. I've done a lot of things to the car since I bought it five years ago. Before that it was in a collection. The existing plug is an Autolite 35 which is not standard for the car and may be as much as twenty years old. I assumed it was a cold plug based on the way the car was set up (street racer) when I purchased it.

Over time, I've been making it driveable for cruise nights. Gone are the 4:10 gears, gone is the full race cam so that I could get enough vacuum to install power disk brakes. More recently I re-cored the rad with a high efficiency core and it runs 20+ degrees cooler (170- vrs 190+).

This is what I've figured out. Tell me if I'm right or wrong.

• High operating engine temperatures result in the need for a cold plug.
• High operating temperatures can be the result of equipment and/or vehicle use.
• If plug fouling is white, colder plugs should be used; if fouling is blackish, hotter plugs should be used.

Base on comments here and elsewhere I'm going to install standard plugs. I'm rarely operating the car at high engine temperatures and the fouling on the current plugs is blackish. If the problem persists, I'll go with hotter plugs.

 

[OldFolksMopar]

Hey Ron, have you pulled the distributor cap lately? You may surprised as to what you find. Might not be a plug issue. Just my 2 cents. Larry

 

[RJRENTON]

Gentlemen,
Spark plugs are simple but complex items. What the factory installed was basically a compromise for general use....a combination of "city" (50% driving) & "highway" (50%) driving. A nominal heat range for a given engine, say a 383 cubic inch Roadrunner 335hp, in stock configuration would be a Champion J-11Y or P-34P Mopar. For those guys that "hate" Champion plugs, the brand of their choice is OK, but the important consideration is engine. Factors such as fuel mixture, octane rating, fuel distribution, spark advance (both initial and total), RPM, all influence spark plug type and heat range.
I can only speak of my application. My RS23V '70 GTX's engine 440 (0.030" bore) has 11.0:1 TRW pistons, fitted at 0.004", Crane cam (equal to the Mopar 292 degree, .509 lift), Prestolite dual point distributor, plus rejetted carbs, 4.10 Dana, built for "street" use. The plugs I use are Cnampion UJ-11G (non projected insulator tip and non resistor) with the G suffix for gold paladium alloy electrode OR Champion HO-8A pure platinium electrodes. The HO-8A plugs were developed by Champion for a niche application for Homelite racing 2 cycle go cart engines running a fuel mix of methanol-nitromethane and castor oil at 10,000 RPMs. Why such special plugs????? Answer: because they work for me. They are not made any longer...I buy them when and where I can find them....just about all the folks selling them have no idea what they are for.....I have a large supply of both types stashed away. These plugs last for years due to the materials used in the electrodes. Would they work in your application???? That must be detetmined by you.....I only know what works for me. One must "read the plugs" - cylinder by cylinder to determine mixture and distribution patterns. Combustion chamber temperature is the biggest influence on spark plug heat range selection...error on the cold side....fouled plugs are easier to fix than a melted piston....the old addage of "caviet emptor", paraphrased....let the owner decide....
Cheers,
RJ Renton

 

[Bigal75]

Ngk br7 or 8...try in that heat range. You can tell by the first few threads of the plug. You should have a couple of threads that discolor with heat.

 

[Dennis H]

ngk's.